Effects of nonuniformity factor on the impulse breakdown voltage characteristics of SF6 gas and with a spacer

Investigations were carried out on the breakdown characteristics of a nonuniform field gap, with and without spacers, under impulse voltages in the SF₆ environment. Both lightning impulse (LI) and switching impulse (SI) voltages were considered. In a highly nonuniform field, the presence of the spacer did not change the breakdown voltage characteristics significantly. With SI, for positive polarity, the spacer efficiency was observed to be greater than one. However under a moderately nonuniform field, the presence of the spacer appeared to distort the field distribution considerably, which was manifested in the breakdown voltages characteristics. The surface charge which occurred on the insulating surface probably changed the moderately nonuniform field into highly nonuniform field conditions. The results of these investigations are discussed